An estimated eight million Americans suffer chronic low back pain due to disc problems requiring a total disability health care expenditure of over twenty billion dollars. The interverebrate disc can be looked upon as an osmotic system. .[.Bacuse.]. .Iadd.Because .Iaddend.of a breakdown of macromolecules as a person ages, the number of particles in the internal softer tissue of the disc, known as nucleus pulposus, increases and causes a rise in osmotic pressure, which in turn causes a fluid influx into the disc and raises the intradisc pressure. Concomitantly, fissures begin to form in the fibrous annulus, which defines the outer periphery of the disc, because of the biomechanical forces placed upon it. Accordingly, the intervertebral disc may extend through the annulus thereof and compress nerve roots, causing great pain. The remedy has been in the past to reduce the mechanical forces that were causing the increase in disc pressure by placing the patient in bed. When such conservative therapy failed, the surgical approach was followed.
A current surgical approach aims at a total disc removal through a partial hemilaminectomy and thus entails the risks that are associated with major surgery and general anesthesia. In addition, costs of this surgery and the in-hospital convalescence required are large.
Chemonucleolysis has been tried to avoid these problems. The intradiscal pressure is decreased by the percutaneous introduction of chymopapain into the intervertebral disc to dissolve it. Such an approach is effective in the majority of patients but does has some side effects, as some patients are hypersensitive to the drug.